Conditioning and finishing absorbent webs



March 6, 1945. w OSGQOD, JR 2,370,811

CONDITIONING AND FINISHING ABSORBENT WEBS Filed June 28, 1940 PatentedMar. 6,

CONDITIONING AND FINISHING ABSORBENT WEBS Harry Whitney Osgood, In,

assignor to S. D. M8585,

Westbrook, Maine,

Warren Company, Boston, a corporation of Massachusetts Application June28, 1940, Serial No. 343,052:

3 Claims.

This invention relates to methods for conditioning and finishingabsorbent flexible webs, e. g. webs of fabric, paper, regeneratedcellulose, or the like, involving moistening the web by applying steam,substantially free from non-condensable gas, to the free surface thereofwhile the other surface is in contact with a heat conducting body, suchas a metal roll, capable of abstracting heat from the web. This methodof moistening webs, and particularly webs of paper, has manyapplications some of which will be described hereinafter; for example,the moistening may serve to determine the moisture content of the paper,or to control the finish produced on the paper by a calendering orsupercalendering treatment, or to control the tendency of the paper tocurl, etc., or two or more of these objectsn It is known thatpaperhaving a relatively high moisture content will fold better andgive lesstrouble from curlingv and from electrostatic charges than paper of lowermoisture content. Paper having a high moisture content has lesstendency; under changing atmospheric condimoisture content, whenconditionedat normal moisture content, most printing papers haveheretofore been finished with a moisture content betions, to developwavy edges than paper having a lower moisture content. Paper having ahigh press room humidity, comes to equilibrium by loss low that desiredby the printer because papermakers have found it difiicult to producepaper having a high and at the same time uniform moisture content. Thisis because the paper web on the paper machine customarily is dried'bybeing passed over a series of heated rolls and in spite of the fact thatintelligent efiorts have been made to secure uniform heating the papergenerally does not dry evenly across the web. The

edges of the web tend to dry out more than the middle portion and in thecase of a wide paper machine two or more relatively moist stripsseparated by relatively dry strips may be found between the relativelydry edges. When suchpaper is calendered the relatively moist strips orstreaks tend to blacken or over-finish producing a defect in the paper.In order to avoid this difficulty it v is customary to over-dry thepaper and the resulting paper product does not have the high moisturecontent desired.

By the present invention the effects of overto a low moisture content asis customary andthen a predetermined quantity of water is distributeduniformly throughout the paper and upon its surface by condensing steamin and upon the web while it is moving in contact with .a heatconducting body at a temperature below that necessary to condense steam,e. g. below 1 90 F. and preferably within the range from F. to F. Theheat conducting body may be a metal roll provided with means forcirculating a cooling fluid, e. g. water, through passages therein. Formost effective moistening substantially pure steam at a temperature 01'about 212 F. should be used; i. e., the steam should be substantiallyunmixed with uncondensable gas and free from water in liquid form. Thesteam must, of course, be uniformly distributed as will more fullyappear hereinafter. The moistening treatment may be applied to the paperat any time after it has been dried, e. g. just as the paper leaves thedrier, or immediately after calendering, or as the paper is being fed toa rewinder or to a sheet cutting machine. In accordance with theinvention moistening may be made to assist in improving the density andapparent formation of the paper and the compactness and levelness of thesurface in addition to the other effects mentioned above.

When the chief or sole purpose is to increase the moisture content ofthe paper it suffices to pass the web about a heat-abstracting roll orequivalent device so positioned that the side of the device covered bythe web is adjacent to or projects into a steam-box supplied with steam.Such an arrangement is shown in Fig. 3 to be described hereinafter. Thequantity of moisture ferred, however, that the steam be blown against asurface of the web at close range while the revers side of the web is incontact with a cooling surface. By impinging a uniform ribbon-likecoated and I with a jet of steam from the Jet of steam across the widthof the sheet the quantity of steam used can be carefully controlled andinstantly varied at will. Besides ease of control, however, steaming bymeans of an impinging jet affords other advantages as will be explainedhereinafter.

Illustrative processes in accordance with the invention will bedescribed in connection with the accompanying drawing which illustratesspecific apparatus embodying the invention:

In the drawing:

Fig. 1 illustrates the moistenlng device in connection with asupercalender;

Fig. 2 illustrates the moistening device associated with a machinecalender;

Fig. 3 illustrates an alternative form of moistening device.

Fig. 4 is an enlarged perspective view of a portion of the steam nozzleshown in Fig. l, and

Fig. 5 is an enlarged perspective view of a portion of the steam nozzleshown in Figs. 2 and 3.

Referring to Fig. 1, 5 is a supercalender of standard constructionconsisting of alternate hard or metal and soft or yielding rollsdesignated by the letters H and S, respectively. I is the paper webwhich moves, as indicated by the arrows, from the storage roll 2 overthe guide roll 3, past the steaming device 4 to the calender stack 5. 6and 6' are fly rolls which usually are employed in treating coatedpaper, but are not ordinarily used in treating uncoated paper. From thelast nip in the calender stack the paper passes over roll I which isprovided with means for cooling it (not shown); for example, it ishollow and connected with means for circulating cold water through it.It is observed that the side of the paper web facing the steaming device4 contacts the hard rolls of the supercalender and the other side whichhas contacted the soft rolls faces the steaming device 8. The web thenpasses over the guide roll II and is wound on the reel l2. 9 is a shieldaround the steaming device 8 to prevent the escape of steam into theworkroom. The steamer 8 and shield 9 are movably mounted on a support l0so that they may be swung out of the way when threading the machine.

Referring to Fig. 2, A represents the drier section of a paper machine,B the first calender stack, C a second calender stack, and D the windupreel. In the drier section A, the paper web I is dried to a uniform lowmoisture content, preferably below 3% in the case of book paper, andthen passes through one or more nine of the first calender B which is amachine calender of standard construction with all hard rolls, and thenpasses on to the calender C, the rolls of which are all hard. The web isshown passing through three nips of the calender B. Rolls 13 and Il arehollow or bored and provided with means (not shown) for circulating acooling fluid through them. The remainder of the rolls of calender C maybe of standard construction. The paper web passes down through the stackand over the roll [3 where its free face is contacted steamer 2|; thenit passes between rolls I3 and I4 and around roll 14 where its otherface is exposed to the steamer 2| and then on through the final nip ofthe stack to the winding reel D. It is noted that in the above describedoperation the paper web passes through a nip of the calender stackimmediately after steaming and While its surface still carries the filmof moisture applied by the steaming device 2|. The steamers 2i and 2!are each provided with hoods 22 and 22' which 'may be connected toventilators (not shown) to prevent escape of steam into the workroom.Steamers 2| and 2| may be movably supported as described in connectionwith Fig. 1.

In Fig. 3 a paper web I passes about cooled roll 15. A portion of rolll5 covered by the paper web extends into a steam-box l6 filled withsubstantially pure, dry steam which enters the box through pipe I!controlled by valve 18 and the rotatable nozzle l9 which may be directedat any angle, either toward or away from the paper. Steam contacting thecooled web inside the box condenses, chiefly on the surface of thepaper. Condensate collected inside the box escapes through drain 20.When nozzle is is turned so that its jet does not impinge against thepaper the device acts merely as a steam-box and in that event, at least,the box should closely fit the paper to prevent excessive leakage ofsteam.

A suitable steaming device must assure the de liverance of steam ofsubstantially uniform pressure and quality across the entire width ofthe sheet. In case a jet is used to give velocity to the steam impingingon the sheet it must deliver a substantially uniform jet or ribbonacross the width of the sheet, i. e. the size, shape, velocity andcomposition of the jet must be uniform; the steam must be free ofparticles of water of appreciable size which, .if present, will resultin imperfections in the paper; the steam must be substantially free ofdilution; the jet preferably should be delivered at a substantialpressure and contact the paper at sufiicient velocity to penetrate thepaper and displace air therefrom. The jet should be fiat andnon-divergent. It has been found that steam at a nozzle pressureapproaching 1 pound per square inch delivered from an orifice about /8inch wide positioned at not more than about 1 inch from the paper givessatisfactory results. The jet in order to afford any appreciable eflectfrom velocity should strike the paper at a velocity of at least about 5feet per second and preferably at a velocity of about 25 etrate andcondense in the paper when delivered from a. narrow orifice at'highvelocity than when delivered from a wide orifice at lower velocity.

Suitable steaming nozzles are shown in Figs. 4 and 5. Referring to Fig.4 the nozzle consists of a cylindrical pipe 23 provided with a slitorifice 24 and a steam supply pipe 25 extending through the pipe 23 andhaving outlet orifices directed away from the slit 24. This arrangementserves to trap any drops of water carried by the steam and also toprovide a uniform distribution of the steam to the slot. This 'nozzle isof the known,

contacted while being steamed preferably is in the form of. a, metalroll as illustrated, but any other suitable cooling surface, such as astationary surface over which the paper slides, may be employed.

By controlling the temperature of the cooling surface and the size andimpinging velocity of the steam jet, any desired quantity of water up to10% or over, even up to 20% or more for some yp s of paper, may be addedto the paperby a single steaming operation. If more moisture is desiredthan can be obtained in one passage through the apparatus, two or moreof the devices may be used in succession to condense additional steam inthe web. For printing paper the desired final moisture content usuallydoes not exceed 10% and in most instances about 6% to 7% issatisfactory. Since the paper generally has a moisture content prior tosteaming of about 2 to 3% this means that up to 8% and generally about3% to of moisture must be added by the steaming operation.

In practically all cases at least 2% of water is added by the operation.

It is known that when one surface of a paper sheet is moistened and themoisture is allowed to evaporate from that surface, the sheet will tendto curl towards the treated surface. In some cases such a tendency tocurl is desirable as when it is used to counteract an existing tendencyto curl in the reverse direction; in some cases, of course, a tendencyto curl is undesirable. steaming a free span of paper, which is not incontact with a cooled roll, as has been done to remove the reverse sidefinish and curl of one side supercalendered paper, it is known that thegreater is the steaming the more pronounced is the effect on curl. Butit has been found that even very severe steaming according to the priorpractice described adds not over about of moisture to the paper. Incontradistinction to this, by steaming in accordance with the presentinvention while the paper is backed by a conductive surface at belowabout 190 F. and preferably at from about 100 F. to 140 F. any desiredquantity of moisture within reason may be added to the paper, andmoreover the moistening operation may also serve to control the finishand curl o'f-the paper. At first thought, since the amount of water inthe paper and the degree of curl inthe paper are independent variables,

it might seem difficult or impossible to control both in a singleoperation. However, it is found that the quantity of steam condensed inthe web may be determined as desired by controllingthe temperature ofthe cooling roll, while the tendency to curlis found to depend largelyupon the depth within the sheet at which the condensation takes place,and so may be varied at will by varying the velocity of the steamimpinging upon the web. In general the higher the velocity of the steamimpinging on the web the deeper is the point of condensation in thesheet and the less tendency is there for sheet to curl towards thesteamed side.. For example, paper treated in the apparatus shown in Fig.3 with the jet pointed away from the paper will develop a strongtendency to curl toward the moistened side, but paper treated by steamof high velocity from the jet shown in Fig. 1 can, if desired, beproduced without developing any appreciable tendencyto curl, or with anydegree of curl wished for. This simultaneous control of curl andmoisture content is entirely novel and is I before or after its secondpassage through the supercalender because only a small amount of wateris expelled from the paper by each passage.

of the paper through the supercalender and enough water may be added atthe start to compensate this loss. Or moisture may be added to the paperafter its first passage through the supercalender. On the other hand, ifsuch a high moisture content in the finished paper. is desired that thepresence of this amount of moisture in the paper duringcalendering wouldresult in blackening. it may be necessary to add part of the waterduring or after the second supercalendering. When it is necessary to addmoisture to the paper after supercalendering and this addition ofmoisture tends to lower the finish of the paper, this loss of finish canbe compensated by giving the paper, before the final mois tenin a higherfinish than is desired on the paper product.

The following is illustrative of the moistening effects obtainable. Ahighly filled book paper weighing 40 pounds per ream (25 x 38-500sheets) containing 3.1% moisture was lightly steamed, thensupercalendered, and then steamed on the reverse side giving a moisturecontent of 6.1%. The paper was then passed through the '40 supercalenderagain to finish the reverse side,

without further steaming, and showed a final moisture content of 5.5

The paper may be steamed after partial calendering and then while theapplied film of mois ture is still on the surface of. the paper it maybe passed between pressure rolls with the wet surface contacting a hardroll. As stated the steam ing may be done against the calender rollsthemselves, provided they are designed to be cooled,

or against special cooled fly rolls inserted at any desired point in thepath of the paper. A preferred embodiment of-the invention, however, is

that illustrated in Fig. 2 in which at least two of the rolls of acalender stack are designed to tively large amount of water added to itimmediately before being calendered and still show no excessiveblackening after calendering. Paper, moistened by the present method,may be densified and its look-through properties considerably improved.It may be provided with a very level surface and a gloss finish.

When the invention is practiced in connection with a machine calender,paper having improved" printing qualities is obtained the finish ofwhich may be anything desired from a medium machine finish to a finishhigher than that ofso-called English finish paper, these propertiesbeing associated with the desired high and uniform moisture content.

The quantity of moisture added to the paper can be positively andaccurately controlled by regulating the temperature of the cooling rolland/or the velocity of the jet and the distance of the nozzle from thepaper. In general, the moistening is more efiective in giving-thedesired finish with a given pressure on the rolls and a given number ofnips than other methods of moistening the paper. For example, to producea machine or English finish it is generally sufficient to employ one ortwo nips after moistening at normal roll pressures. By employing greaterroll pressures after the moistening, densification can be carried to thepoint at which the paper is more or less translucent and resemblesparchment in appearance. In fact, especially when using a supercalender,glassine paper can be made from a suitable glassine stock without thecustomary seasoning before calendering.

In producing printing paper, blackening must be avoided and this may bedone by keeping the temperature low during th calendering of the moistpaper. The permissible temperature depends somewhat on the moisturecontent of the paper, but the rule may be stated that the temperature ofthe calender rolls should not exceed 150 F. in the treatment of bookpaper containing more than 6% of moisture. In the preferred temperaturerange of about 100 F. to about 120 F., it is possible to calender bothcoated and uncoated paper without excessive blackening at a moisturecontent of 10 to 12% and even higher in the case of ground wood paper.

The following examples of specific treatments of paper are illustrative:

Example 1.In an apparatus like that illustrated in Fig. 1 paper weighing'70 pounds per ream (25 x 38--500 sheets) and having on one side a15-pound mineral coating was steamed lightly on the coated side justbefore entering the supercalender with the coated side contacting thehard rolls. From the last nip of the super calender the paper was takenaround the metal rolls I maintained at 110 F. with the high finishedside against the roll and the low finished side contacting another steamjet. The paper speed was 650 feet per minute. The moisture content ofthe paper after the first steaming and before entering the supercalenderwas 4.7% and after the second steaming 6.6%.

about feet per second. The low finish side of the paper was practicallyfree of finish and the paper was practically free of curl.

Example 2.In an apparatus like that illustrated in Fig. 2 a highlyfilled book paper of pounds per ream (25 x 38-500 sheets) came from thedrier section A with a, moisture content of 3% and was given three lightnips in the calender B to smooth out gross irregularities in the web andto take out some of its stretch as is generally done before passing thepaper to the finishing calender. The paper then passed through threenips of the calender C. The surface temperature of rolls l3 and I4 was125 F. and steam was delivered by steamer 8 against the paper at avelocity of 20 feet per second and by steamer 8' at a velocity of 25feet per second. The speed of the paper was 470 feet per minute and thepressure on the bottom nip 390 pounds per inch of The steam jet wascontacted with the paper at a velocity of paper width. The finishedpaper hada moisture content of 6.7%, a high English finish, was free ofblackening and had a bulk or .0119 inch for 4 sheets.

In the foregoing examples the invention has been described in connectionwith a supercalender (Example 1) and a machine calender (Example 2). Theinvention is particularly useful in producing one-side coated anduncoated one-side supercalendered paper such as is widely used forlithographic printing in which use a high moisture content is desirable.Such paper can be produced of any desired moisture content and in whichcurl is controlled to any desired degree.

When paper is printed in more than one color it is necessary for thepaper to receive more than one impression. In many cases there is aconsiderable time interval between the successive printings. If thevarious .impressions are to be in register and give satisfactory resultsit is of vital importance that the paper shall not change in shape ordimension during the interval between impressions. Ordinarily it hasbeen the custom. when paper was to be printed with several impressions,for the printer to hang the paper for a period of several hours in theatmosphere of the print shop, in order that the paper may come toequilibrium under the atmospheric conditions of the press-room and sonot change in dimensions or go out of shape during the printingoperation. The printer says that by so doing he conditions" the paper tothe atmosphere of the pressroom.

A successfully achieved object of the present invention was to pre-treatpaper during its manufacture so that it could be delivered to theprinter containing approximately the desired quantity of water and insuch condition that it could be printed immediately and still not go outof shape more than paper actually conditioned by exposure to thepress-room atmospher before printing. The simplicity of the process ofthe invention obviously makes it very advantageous in comparison withthe troublesome and timeconsuming method of exposing the paper to ahumid atmosphere to take up moisture. Moreover, in the case of one-sidecoated or one-side supercalendered paper the process has a particularadvantage in that all the moisture is added through the unfinished sideof the sheet and so avoids all liability of damage to the high finishedside as may well be encountered in cases where both sides of the web areexposed to a very humid atmosphere. This feature of the invention itselfis of considerable importance.

Unexpectedly, as has been shown by repeated printing tests, papersconditioned according to the process of the invention have actuallygiven better results than papers conditioned by hanging in thepress-room atmosphere. Even more surprisingly it has been found thatpaper conditioned according to the invention so that it contains arelatively high moisture content, say an amount that would be equivalentto that required for equilibrium with an atmosphere of 50 to 65%relative humidity, may be printed directly, without press-roomconditioning, in atmospheres the moisture contents of which vary in awide range, say from 30 to 65% relative humidity, with excellentresults. This is a wholly unobvious result given'by the invention. Theentire reason for the superior results mentioned is not fully understoodat present. Drying the paper to a uniform low water-content as one stepin the operation apparently contributes to the result. Possibly adding asubstantial quantity of moisture while holding the paper under tensionis another contributing factor, or perhaps it is a fact that condensingmoisture deep within the web acts to release strains and equalizetensions therein to an extent that on later exposure to varying humidityconditions the sheet reacts less than might be expected. Whatever thetrue explanation of the phenomenon, the fact remains that the processdescribed yields excellent results and is undoubtedly a valuable advancein the paper making art.

In the use of the machine calender as illustrated in Example 2 it ispossible to employ only one cooled roll and one steamer and to producepaper having only one highly finished side. It is also possible tolocate the cooled rolls at other positions in the stack and that thepaper may pass through nips of the stack before or after, or both beforeand after, contacting the cooled roll or rolls, or instead of using aroll of the stack as the cooling roll, a fly roll may be employed forthis purpose. Thi eliminates the danger of damage to the soft rolls ofthe supercalender by water which might condense on the ends of thecooled 7 metal roll outside the width of the paper. The

apparatus illustrated in Fig. 2 is designed for calendering uncoatedpaper in the continuous production of paper on the paper machine. butcoated paper also may be calendered with steaming in the same way on anall-metal roll calender.

This application is a continuation-in-part of my application Serial No.160,681, filed August 24, 1937.

I claim:

1. Process which comprises drying a paper web to a uniform, low watercontent and then increasing the water content of the web by moving thedried web in contact with the surface of a cooled metal roll maintainedat a, temperature below 190 F., impinging a ribbon-like jet ofsubstantially pure dry saturated steam with a portion of the surface ofthe web opposite that in contact with the cooled metal roll at avelocity of at least 5 feet per second and at an angle approaching theperpendicular to the web from an orifice positioned not more than aboutlinch from the web, thereby avoiding substantial entrainment and mixingof air with the steam at the line 01 contact with the web and condensingthe steam in the web to increase its moisture content from about 2 toabout 20 percent by weight of the dry web.

2. Process as defined in claim 1 in which the cooled metal roll ismaintained at a temperature between F. and F.

3. Process as defined in claim 1 in which the velocity of the steam isat least 25 feet per second.

HARRY WHITNEY OSGOOD, JR.

